Field of the Invention
The present invention relates to the sector of valves for inflating tyres of tyred wheels, in particular tyres for vehicles, wherein the term “vehicles” refers to motor vehicles, vans, trucks, motorcycles or in general means of locomotion on tyres.
More in detail, the invention relates to a controlled tightening metal valve of the clamp-in type designed to be used in the context of TPMS (Tire Pressure Monitoring System) technology, in which electronic sensors for the detection and transmission of certain tyre operating parameters, in particular pressure, but also temperature, for example, are mounted directly on the valve itself and the valve is fixed to the wheel by means of a hole made in the rim.
Description of the Related Art
Metal valves of the clamp-in type generally consist of a shaped head, usually cylindrical or semispherical or polygonal, which is associated with a transducer containing the electronic sensors, and of an elongated stem (or rod) to enable the tyre inflation/deflation operations and to fix said valve to the wheel rim by means of specific screw fastening means.
Said screw fastening means generally consist of a nut which screws onto a thread obtained on the portion of the valve stem projecting outside the rim.
Operationally, the valve and the transducer are first joined together in a valve-transducer assembly by means of a perforated fixing screw. Said screw is generally provided with a square head, and is adapted to axially block the head of the valve in a specific complementary seat provided in the transducer.
At a later stage, the valve-transducer assembly is positioned on the wheel rim so that the valve projects outside the rim and the transducer is housed within the tyre, and rests on the inner flange of the rim, so as to be tangential to said rim and thereby reduce the possibility of coming into contact with the tyre during mounting and un-mounting operations.
Said valve-transducer assembly is tightened onto the rim by means of a nut that, by screwing onto the stem of the valve, brings the transducer into contact with the head of the valve and therefore with the head itself, with the interposition of a seal gasket, on the inner edge of the rim.
These valve-transducer assemblies have several limits and disadvantages.
Metallic valves of the clamp-in type are subject to possible damage during final tightening of the nut with which the valve-transducer assembly is fixed to the rim: an improper dosing of the tightening force risks causing the axial rotation of the entire valve-transducer assembly, thus dislodging the transducer out of its seat with respect to its correct position tangential to the rim. Even a minimal rotation of the transducer risks damaging it, for example when changing the tyre.
Furthermore, the centrifugal forces involved and the vibrations of the vehicle when moving can increase the risk of the transducer unscrewing from the valve, if the two components are not securely fixed to one another, or can even cause the nut to loosen.
Moreover, assembly operations, first of the valve onto the transducer, then of the valve-transducer assembly onto the rim, may become disadvantageously long and complicated, given the number of parts involved and the fact that they often need to be manipulated in the confined spaces of the rim, and do not always guarantee the safest, most correct positioning of the components.
Patent application EP 12 77 601 A2 discloses a valve-transducer assembly that tackles these problems, wherein the transducer and the valve body are pre-assembled by means of a fixing screw, the square head of which couples with a seat, having the same shape, belonging to the transducer and the stem of which screws into the valve body.
Tightening of the transducer onto the valve body is completed during the initial phase of tightening the valve onto the rim, which is achieved by means of a specific nut, which can be screwed onto the stem of the valve.
The inside of said nut is provided with a projecting annular element adapted to break while screwing the nut onto the stem of the valve, only when a particular tightening torque is reached, corresponding to the force necessary for the correct tightening of the transducer onto the head of the valve.
Once the projecting annular element has broken, then proceeding with screwing the nut, with higher torque levels, serves to fix the valve-transducer assembly thereby obtained onto the rim.
The solution of providing an annular element with controlled breakage inside the nut to indicate that a certain tightening torque has been reached, although it resolves the aforementioned problems, appears to be complex to manufacture.
In practice, obtaining this annular element by means of a tool working directly on the inside of the nut is not simple, and it is even less easy to guarantee that said element has the precise resistance to breakage that is actually desired.
Operations to check and verify this element on the inside of the nut present difficulties due to the limited amount of operational space available and, therefore, to the limited accessibility to the working and measuring zone.
In the assembly phase too, the possible accidental or imprecise breakage of this element might not be easily visible to the operator.
In the event that said valves are made of aluminum and need to be surface treated to withstand environmental corrosion, application of the protective layer to the inside of the nut could be made even more difficult by the presence of said annular element which, when it broke, would leave a portion of untreated metal exposed.
The constructive disadvantage and reduced reliability of the solution proposed by the aforementioned patent application is therefore apparent.